1. Field of the Invention
This invention relates to a class of vibratory rotation sensor in which the vibrating member is a thin-walled hemispherical shell, and more specifically relates to the electrical connections for such a sensor.
2. Description of Related Art
A conventional vibratory rotation sensor 10 is illustrated in FIG. 1 in an exploded view, as having an outer member 12, a hemispherical resonator 14, and an inner member 16, all of which are made of fused quartz and are joined together with indium. This particular type of vibratory rotation sensor, which has a vibrating member 14 that is a thin-walled axi-symmetric hemispherical shell, is known as a hemispherical resonator gyro (HRG).
The inertially sensitive element in the HRG 10 is the hemispherical resonator 14, usually a thin-walled, bell-shaped object positioned between an outer member 12 and an inner member 16 and supported between the inner and outer members by a stem 26. The thin-walled axi-symmetric hemispherical shell 14 oscillates in one of its lower-order flexing modes. The shell resonator flexing mode takes the form of an elliptical standing wave.
The elliptical standing wave contains four anti-nodes and four nodes, the anti-nodes and nodes being separated from one another by 45 degrees. The rotation sensitivity of the standing wave results from the fact that each mass element of the shell undergoing oscillation acts much like a Foucault pendulum attempting to keep the direction of its linear momentum fixed in inertial space when the shell rotates about its axis. The resulting Coriolis forces, the product of the shell""s vibratory motion, and the inertial input rate, cause the standing wave to precess with respect to the shell. The standing wave precession angle is known as the gain of the gyro.
In operation, forces are required to control the standing wave on the hemispherical shell resonator 14. These forces are quasi-electrostatic in nature. In the case of the HRG 10 in FIG. 1, a number of electrodes 22 are metallized on the inside surface 20 of the outer housing 12, which is concentric with the hemispherical shell resonator 14. The outer surface of the shell resonator 14 is metallized so that when the device is assembled, the electrodes in the outer housing 12, together with the surface of the resonator they face, form a series of forcing electrostatic capacitors. Voltages applied to the appropriate combinations of these electrodes control the amplitude of the standing wave and also act to suppress unwanted quadrature effects.
Rotation of the HRG 10 about an axis normal to the plane of the rim 34 of shell resonator 14 causes the standing wave to rotate in the opposite direction with respect to the HRG 10 by an angle proportional to the angle of rotation of the HRG 10. Thus, by measuring the angle of rotation of the standing wave with respect to the HRG 10, one can determine the angle of rotation of the HRG 10. The vibrational mode of the shell resonator 14 is excited by placing a DC bias voltage on the resonator and an AC voltage on the forcing electrodes 22. The frequency of the AC voltage is usually about twice the resonant frequency of the hemispherical shell resonator 14.
Readout signals from the HRG 10 containing information about the amplitude and location of the standing waves on the shell resonator 14 are also obtained capacitively. The capacitive readout electrodes 24 are formed proximate to a metallized interior surface 30 of the shell resonator 14, where a plurality of electrodes 24 which are located on an inner concentric quartz housing held in close proximity to the inner metallized shell resonator 14. Because of the shell""s oscillating deformation, the capacitance of each of the electrodes 24 is modulated at the resonator flexing frequency. An electronic readout circuit measures these capacitance changes and hence the location and amplitude of the standing wave is determined.
This HRG construction is inherently highly reliable. Its internal electronics consist solely of passive capacitive electrodes sealed in a vacuum. The capacitive electrodes are formed from metallized quartz and a vacuum dielectric between the metallized electrode surfaces, and hence are extremely reliable. Additional and more specific details of vibratory rotation sensors can be found in U.S. Pat. No. 4,951,508 issued to Loper, Jr. et al. Aug. 28, 1990, the entire disclosure of which being incorporated herein.
There are situations where it is desirable to isolate and protect the HRG from external elements. In these situations, it is sometimes necessary to place a hermetic header around the gyroscope to seal out the external elements. In order to obtain the measurements from the capacitive electrodes in the gyroscope, an electrical connection must be established through the hermetic header to the circuits in the gyroscope. It is critical that this electrical connection provides a high degree of mechanical isolation between the gyroscope and the hermetic header, so that this connection does not hinder or restrain the vibrational movement of the gyroscope. Without maintaining such mechanical isolation, the accuracy of the gyroscope measurements can be significantly diminished.
The present invention provides an electrical connection between a vibratory rotation sensor and a hermetic header, wherein the electrical connection maintains a high degree of mechanical isolation between the sensor and the header. The electrical connection includes an electrical pin which is connected to an electrical contact pad on the sensor through a coil spring in order to provide an electrical path for readout information from the sensor. The electrical pin forms an interference fit with the coil spring. The electrical pin includes an enlarged portion having a maximal dimension which is greater than an inner diameter of the coil spring for providing the interference fit between the coil spring and the pin. The degree of interference between the pin and the coil spring can be variable selected by selecting the dimensions of the enlarged portion of the pin and the coil spring, such as the maximal cross-section diameter of the enlarged portion, the length of the enlarged portion, the inner diameter of the coil spring, and the spacing between the coils of the coil spring. Furthermore, by selecting the location of the enlarged portion along a length of the pin, the degree of mechanical isolation between the header and sensor can be variably selected by selecting the amount of active coil extending between the sensor and the enlarged portion of the pin. In this manner, the connection between the electrical pin and the coil spring of the present invention is designed to provide this high degree of mechanical isolation from the sensor while still providing an accurate and reliable electrical connection.